Locking means for electrical plugs



y 1954 H. /HUBBEL| ETAL LOCKING MEANS FOR ELECTRICAL .PLUGS Filed March 3, 1950 Patentecl July 13, 1954 LOCKING MEANS FOR ELECTRICAL PLUGS Harvey Hubbell, Long Hill, and Joseph F. Healy,

Wcstport, Conn., assignors to Harvey Hubbell, Incorporated, Bridgeport, Conn, a corporation of Connecticut Application March 3, 1950, Serial No. 147,361

3 Claims.

ifhis invention relates to plug connectors for electric circuits, particularly to locking devices for securing such plugs against withdrawal from ieir associated receptacles, and an object is to provide an improved locking device for use with plug type connectors.

A further object is to provide a locking device for plug connectors having an improved safety construction which avoids any exposure of live parts on the exterior either of the plug or the assoeiate receptacle, so that there is no danger of any such parts being touched by a user.

Che specific aspect of the invention relates to locking devices for plugs used with three conduct-or cables which frequently have metallic sheaths, and a further object is to provide a looking device constructed and arranged to form part of the grounding connection between the neutral contact blade of the plug and the metallic shell on the plug and the metallic cable sheath, thereby grounding the locking mechanism and eliminat ing the possibility of exposed live parts on the plug.

With the foregoin and other objects in view, we have devised the construction illustrated in the accompanying drawin forming a part of specification. It is, however, to be under- Wd the invention is not limited to the specific details or construction and arrangement shown, but may embody various changes and modifications within the scope of the invention.

this drawing:

i g. i is an end view or elevation of a plug connector constructed in accordance with one embodiment 01"- this invention;

2 is a partial section on the line 2-2 of Fig. l

Fig. 3 is a transverse section on the line 33 of Figs. 1 and 2;

Fig. 4 is a section showing a ground connection to the metallic cover on the plug of Figs. 1 and 2;

5 is a perspective view of the locking mechanism shown in Figs. 1, 2 and 3 with parts broken away, and

6 is an elevation looking from the bottom of Figs. 2 and 3, showing the associated cable in section.

The illustrated embodiment of the invention is shown in connection with an electric plug having a body ll of insulating material surrounded by a metallic cover or shell I2 electrically and mechanically connected to the metallic sheath it of an associated conductor cable I 4. For this purpose a pair of gripping jaws I5 are formed on oppositely disposed, radially movable plates I6 all) slidable in radial grooves I1 formed in the cover I2. Each plate has a gripping jaw i5 which projects through an axial opening it in the cover around the cable I4, which also extends through the opening into the plug body II. Clampi screws 20 extend through cars 2011 on each side of eachjaw it.

The cable it is shown as a three conductor cable. we live conductors 2!, 22 are connected to two contact blades 23, 24 respectively by bindin screws 25, 26 in connecting base plates 2% and 24a to which the contacts are connected and which are secured to the body by the rivets molded in the body. Contacts 23?; and 2d are adapted to engage receptacle contacts 36a. ihe third conductor 2! is neutral and is grounded as hereafter described.

The neutral conductor 2! is connected to a contact blade 32 by abinding screw 32. The contact blade includes a base portion 33 and a pro jecting blade portion 34 which is of U-shaped cross section, and is arranged to engage a bladereceiving contact 35 in a receptacle 3B. The receptacle contact 35 is connected to the neutral conductor 3? of a three conductor cable 33 to which the receptacle is connected. The neutral blade contact 3! of the plug, and the conductor 27 conn cted thereto are grounded to the plug cover it and through it to the cable sheath It by a ground-connecting strip 28 riveted at one end to the base 33 of the blade 3! by the rivet 29 and electrically connected to the cover I2 at the other end 28a by being inserted between the cover and the plug body.

The plug locking mechanism of the present invention is connected to and supported upon the neutral contact blade 3!, whereby it is effectively grounded and no live elements form any part of the mechanism. As illustrated, a flexible reoeptacle-engaging spring finger :II of bronze or other suitable material is secured at one end to the U-shaped blade between the sides and adjacent the projecting end thereof by any suitable means, such, for example, as the rivet Ma. The

1 finger includes an outwardly projecting free end 62 which is inclined outwardly to provide a cam face 52a adapted to be engaged by the end of a threaded bolt or screw 33 extending through an openin :14 in the plug body I I which is shown as extending parallel to the axis thereof. The screw is threaded through the base 33 of the neutral blade 3I and has a projecting head 45 accessible at the outside of the plug body, the head having a screw slot 0]: other means for easy manipulation. Outward movement of the end 42 of the retaining finger 4i into operative locking position is limited by a pair of restraining lugs 47 extending inwardly across the open side of the U- shaped blade from the side walls thereof. By this means the finger is held against being pulled out of the blade by a pull on the plug when the finger is in locking position.

Before inserting the plug in the receptacle the operating screw 53 is retracted to permit the resilience of the locking finger to retract the end 22 thereof into the confines oi the U- shaped contact blade where it is in inoperative position and will not engage the of the receptacle. After the plug is inserted into the receptacle the screw 43 is advanced to cam the end $2 of the finger outwardly into engagement with the adjacent surface 38 or" the receptacle slot 49 into which the blade ill projects, as shown in Fig. 1. In this operative position the finger holds or looks the plug against retraction or removal from the receptacle until the screw is withdrawn sufficiently to permit the finger M to retract under its own resilience and free the receptacle ironi engage ment thereby. As the locking means is inclined as shown the greater the pull on the plug to withdraw the greater the grip on the receptacle.

Inasmuch as the locking mechanism supported upon and electrically connected to the neutral conductor and is grounded on the sheath, there is no exposure of any live part on the outs de or" the plug or the receptacle, and no danger the user touching any live element.

Although we have described a specific embcdimerit of the invention, it will be apparent that it can be variously modified and adapted within the scope or" the invention.

Having thus described our invention, we claim:

[in elect ical plug co" arising a insulating and a p-0jecting contact mounted thereon, locking -neans for retaining against removal from an associated receptacle provided with a recess to which e is inserted compris ng a spring memsee ed to contact ma-dand provided ii a rree edge fac lg toward the body to engrlp a s wall or" recess, .2 rig tending to Shirl, said edge away from s Me wall to r lease he plug, the end porof the spring being inclined to form a cam suilace, and a screw extending through the p: body and accessible for operation from the e:-.

terior thereof and arranged with its inner end engaging said cam surface to $1 it said free edge into locking engagement with said side wall and hold it there to retain the plug in place.

2. An electrical plug comprising a body of insulating material and a projecting contact blade mounted thereon, locking means for retaining said plug against removal from an associated receptacle provided with a recess into which the blade is inserted comprising a spring member secured to said contact blade and provided with a free edge facing toward the body to engage grip a side wall of said recess, said spring tending to shift said edge away from said side wall to release the plug, means extending through the plug body and accessible from the exterior thereof for shifting said free edge into locking engagement with said side wall and holding it there to retain the plug in place, and an ear on said contact extending over the outer side of said spring member to limit outward movement of said member.

3. An electric plug comprising a body of insulating material and a projecting contact blade mounted thereon, a metal sheath enclosing said body, locking means for retaining said plug against removal from an associated receptacle provided with a recess into which the blade is inserted comprising a spring member secured to said contact blade and provided with gripping means adjacent its free end to engage and grip a side wall of the recess to retain the contact therein, said spring tending to shift said gripping means away from said side wall to release the plug, and a screw extending through the plug body and grounded on the sheath, said screw being accessible for operation from the exterior of the plug and engaging and having a camming action on said spring to ground the contact on the sheath and to shift said gripping means into engagement with said side Wall and hold it there to retain the plug in place.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,771,757 Keeper July 29, 1930 1,782,527 Bennett Nov. 25, 1930 2,026,755 Stem Jan. 7, 1936 2,042,633 Richardson June 2, 1936 2,049,093 Thorin July 28, 1936 2,201,578 Grohsgal May 21, 1940 2,309,311 Grohsgal Jan. 26, 1943 2,410,618 Zelov Nov. 5, 1946 2,436,586 Marigold Feb. 24, 1948 FOREIGN PATENTS Kumber Country Date 571,528 Germany Mar. 2, 1933 

